Lighting device

ABSTRACT

An LED lighting device is provided which is capable of being connected to a network and being controlled by a host computer also connected to the network. The lighting device has several lifespan expanding features such as including several extra LEDs such that as the LEDs of the lighting device degrade over time more LEDs can be turned on thus allowing a constant luminosity to be maintained.

BACKGROUND OF THE INVENTION

[0001] The current invention is an light emitting diode (herein referredto as LED) lighting device having multiple features designed to allowthe lighting device to maintain luminosity as measured in candelas, overits lifespan. The invention is also designed so that multiple lightingdevices can be connected in a network controlled by a host computer,such that the general luminosity over an area (e.g. a tunnel) can becontrolled.

[0002] Traditionally, roads and tunnel lighting devices have used usesHID (High-Intensity Discharge) lamps, powered with high-voltage (e.g.300VAC to 400VAC).

[0003] Existing roadway standards divide the length of the tunnel into anumber of regions. Each region requires a lighting intensity (sometimesherein referred to as luminosity) that increases as it is nearer theentrance/exit points (because of the presence of higher illuminationfrom the sun), and decreases towards the middle of the tunnel. As anexample, a typical system can use one 130 W lamp per 1.75 m per roadlane in order to satisfy the daytime specifications required in theInterior Zone of a tunnel.

[0004] A problem with current tunnel lighting lamps is with lifespan. Ina typical tunnel lamp which uses one or maybe two illumination sources,the lighting device can easily become unuseable should the illuminationsource break down. In these cases the illumination sources need to bereplaced manually before the lighting device can again providesufficient light. It also is necessary to close lanes in the tunnelwhile the maintenance is in progress. Thus maintenance of lightingdevices can become costly and time consuming.

[0005] Therefore, a new lighting device which allows for a longerlifespan without maintenance is desired. The present invention attemptsto provide such a lighting device using LEDs as illumination sources.While an individual LEDs is on its own not sufficient to providelighting for a tunnel, LEDs only cost a fraction of what a typical HIDlamp would cost. An LED further uses much less power than that of atypical HID lamp. Therefore, a plurality of LEDs can be provided for alighting device and the cost and power usage would still be below thatof a typical HID lamp. For instance a example LED lighting device couldprovide lighting for the interior of a tunnel, while using 780 LEDs andbeing powered by a 24VDC power supply.

[0006] LED lighting devices are known in the art, though most of theselighting devices are use for making billboards and traffic signals.Examples these kinds of lighting devices can be found in U.S. Pat. No.6,175,342 Nicholson et al., U.S. Pat. No. 6,150,771 Perry, U.S. Pat.Nos. 6,150,996, 5,514,698 Nicholson et al., U.S. Pat. No. 4,357,671Miller, U.S. Pat No. 4,271,408 Teshima et al., and U.S. Pat. No.4,298,869 Okuno.

[0007] Using a plurality of LEDs as a replacement for an standardillumination source is less common, but are for instance described inU.S. Pat. No. 6,255,786 Yen, and U.S. Pat. No. 6,211,626 Lys et al.These lighting devices show that LEDs can be used to replace morestandard illumination sources. They do, however, not have features whichallow for a constant luminosity to be maintained over an extendedlifespan.

[0008] Certain patents, such as U.S. Pat. No. 6,236,331 B 1 Dussurealt,U.S. Pat. No. 6,153,985 Grossman, and U.S. Pat. No. 5,783,909 Hochstein,propose to compensate for long term LED degradation through a variablecurrent. In these lighting devices, which deal mostly with trafficlights, the luminosity output of traffic lights using LEDs is stabilizedby varying the current flow. The lighting devices measure the luminosityoutput of the LEDs and either increase or decrease the current beingsupplied to the LEDs as a result. The current control is usuallyperformed either through proportional DC (Direct Current) control, orthrough PWM (Pulse Width Modulation) of the LED supply. In the contextof roadway or tunnel lighting, the use of PWM to control the LEDintensity may be problematic. This is because it can lead to visiblestroboscopic beat effects in the light superposition of multiplelighting devices each having slightly different, non-synchronized PWMfrequencies.

[0009] It would therefore be advantageous to have a different way ofstabilizing the lighting device's luminosity.

SUMMARY OF THE INVENTION

[0010] Therefore the present invention provides a lighting devicecomprising

[0011] a plurality of groups of light emitting diodes, each of saidgroups of light emitting diodes containing one or more light emittingdiodes, each of said light emitting diodes being configured so as topass between an energized light emitting state and a non-energizedstate;

[0012] luminosity measuring means for providing a standard luminosityreading at predetermined time intervals (e.g. from a test diode);

[0013] controller means for transferring, at predetermined timeintervals, in response to said standard luminosity reading, one or moreof said groups of light emitting diodes between a first energized groupwherein said light emitting diodes are in said energized light emittingstate and a second non-energized group wherein said light emittingdiodes are in said non-energized state.

[0014] In one aspect of the present invention said controller means maybe configured to maintain all of the light emitting diodes in said firstenergized group when a predetermined luminosity reading is provided bysaid luminosity measuring means.

[0015] In one embodiment said luminosity measuring means for providing astandard luminosity may comprise one or more test light emitting diodescoupled to light sensors, such that said test diodes can emit lightwhich will then be measured by the light sensors. This measurement willthen form the basis for said standard luminosity.

[0016] The invention further provides a lighting device comprising

[0017] a plurality of groups of light emitting diodes, each of saidgroups of light emitting diodes containing one or more light emittingdiodes, each of said light emitting diodes being configured so as topass between an energized light emitting state and a non-energizedstate;

[0018] usage time measuring means for providing a usage time measurementfor each of said groups of light emitting diodes at predeterminedintervals (e.g by storing usage times in a memory)

[0019] controller means for transferring, at predetermined timeintervals, in response to said usage time measurements, one or more ofsaid groups of light emitting diodes between first energized groupwherein said light emitting diodes are in said energized light emittingstate and a second non-energized group wherein said light emittingdiodes are in said non-energized state.

[0020] In one embodiment of the present invention said controller meansmay be set to transfer said groups of light emitting diodes between saidfirst energized group and said second non-energized group in response toboth the standard luminosity reading and the usage time measurement.

[0021] It should be clear that the controller means can be configured totransfer said groups of light emitting diodes between said firstenergized groups and said second non-energized group in response to anysuitable criteria.

[0022] In one aspect of the invention the LEDs may always be used atfull current, and the lighting device's luminosity may be controlled byadjusting the number of LEDs turned On.

[0023] This method of using a single current may result in a lower LEDdegradation rate than other methods, because it is known that an LEDused continuously at a fractional current degrades faster than an LEDused for a fractional time at full current, both fractions being equal.

[0024] As an example: data provided by Toshiba, a major LEDmanufacturer, for its TLYH Amber LED series (such as could be used withthe lighting device) indicates that at 25 deg. C. the LED luminositywill degrade by 50% in 170,000 hours when used at 10 mA, and in 140,000hours when used at 20 mA. If the the LED were used at 20 mA only halfthe time (thereby getting the same average light as using itcontinuously at 10 mA), it would take 280,000 hours to reach the 50%degradation point, lasting substantially longer than the 170,000 hoursof the continuous 10 mA option. It can therefore be seen that reducingusage time even while compensating with increased current will provide aslower degradation rate.

[0025] The invention also provides a lighting arrangement comprising:

[0026] two or more circuit board means, each circuit board means havinga projection axis and a plurality of light emitting diodes, such thatany light emitted by the light emitting diodes on each of said circuitboard means is projected substantially parallel to said projection axis;

[0027] said circuit board means being disposed such that each of saidprojection axes are disposed at an angle to each other.

[0028] In an aspect of the present invention said angle may for examplebe from 5 to 15 degrees.

[0029] The invention also provides a network comprising:

[0030] a host computer; and

[0031] a plurality of light emitting diode lighting devices;

[0032] said host computer comprising:

[0033] means for transmitting a request for a status report from each ofsaid light emitting diode lighting devices,

[0034] means for receiving a status report from each of said lightemitting diode lighting devices; and

[0035] means for transmitting a signal to each of said light emittingdiode lighting devices such that the host computer can direct how muchlight each of said lighting devices emits; and

[0036] each of said plurality of light emitting diode lighting devicescomprising:

[0037] means for receiving a request for a status report from said hostcomputer, creating said status report, and transmitting said statusreport to said host computer; and

[0038] means for receiving a signal from said host computer and alteringhow much light said light emitting diode device emits in response tosaid signal.

[0039] In one embodiment said status report may comprise currentluminosity setting, current actual luminosity output, current lightemitting diode degradation, current dirt accumulation, current number oflight emitting diode groups in use, current number of open-circuitedlight emitting diode groups and current average usage time of lightemitting diode groups.

[0040] The present invention further provides a method for manipulatingthe light intensity in a tunnel, said tunnel comprising a lightingsystem comprising a plurality of lighting devices, said methodcomprising means for raising and lowering, in unison, the luminositylevel of each of said devices; (e.g. the means for raising and loweringmay, for example, comprise a computer in a network as described hereinor a suitable switching means or other control means able to accomplishthe desired dimming or increase in light intensity).

[0041] The invention further provides a network comprising:

[0042] a host computer; and

[0043] a plurality of light emitting diode lighting devices;

[0044] said host computer comprising:

[0045] means for transmitting a signal to each of said light emittingdiode lighting devices such that the host computer can direct how muchlight each of said lighting devices emits; and

[0046] each of said plurality of light emitting diode lighting devicescomprising:

[0047] means for receiving a signal from said host computer and alteringhow much light said light emitting diode device emits in response tosaid signal.

[0048] The invention further provides a dirt detection system for atransparent surface, comprising:

[0049] an electromagnetic radiation emitting means for emitting light;

[0050] electromagnetic radiation measurement means for measuring light;

[0051] said electromagnetic radiation emitting means and saidelectromagnetic radiation measurement means being configured such thatsaid electromagnetic radiation emitting means emits a certain amount ofelectromagnetic radiation through said transparent surface, and saidelectromagnetic radiation measurement means measuring how much of saidcertain amount of electromagnetic radiation is reflected by saidtransparent surface and comparing said amount to a base measurementtaken when said transparent surface is free of dirt.

[0052] The invention also provides a light emitting diode lightingdevice, comprising:

[0053] a plurality of groups of light emitting diodes, each of saidgroups of light emitting diodes containing one or more light emittingdiodes, each of said light emitting diodes being configured so as topass between an energized light emitting state and a non-energizedstate;

[0054] memory means for keeping track of the time each of said groups oflight emitting diodes have been in said energized light emitting state;

[0055] energizing means for inducing any of said groups of lightemitting diodes to pass between said energized light emitting state andsaid non-energized state;

[0056] a luminosity measuring system comprising one or more test lightemitting diodes that are equivalent to said one or more light emittingdiodes which make up said groups of light emitting diodes, and measuringmeans for providing a luminosity reading of the light that one or moretest light emitting diodes provide when in said energized state;

[0057] storage means for storing the luminosity reading provided by saidmeasuring means;

[0058] calculation means for calculating the number of said groups oflight emitting diodes which are needed to provide a light of a desiredluminosity, herein referred to as X, said calculation being based on theluminosity reading stored in the storage means;

[0059] partitioning means for temporarily assigning said groups of lightemitting diodes to a first energized group or to a second non-energizedgroup; and

[0060] timer means for causing, every time a predetermined time haselapsed, the luminosity measuring system to provide a new luminosityreading, and the partitioning means to partition said groups of lightemitting diodes;

[0061] said partitioning means comprising:

[0062] means for causing said calculation means to calculate X,

[0063] means for selecting the X groups of light emitting diodes whichhave spent the least amount of time in said energized light emittingstate and assigning them to said first energized group,

[0064] means for assigning the remaining groups of light emitting diodesto said second non-energized group, and

[0065] means for causing said energizing means to induce the groups oflight emitting diodes assigned to said first energized group to pass tosaid energized light emitting state, and to induce the groups of lightemitting diodes assigned to said second non-energized group to pass tosaid non-energized state; and

[0066] the total number of groups of light emitting diodes (X+Y) in thelighting device being such that Y is non-empty for the majority of thelifespan of the lighting device.

[0067] In one aspect the light emitting diode lighting device mayfurther comprise:

[0068] a heat dissipation means for dissipating heat generated by saidgroups of light emitting diodes.

[0069] In one aspect the light emitting diode lighting device mayfurther comprise:

[0070] a light emitting diode status monitoring system having means formonitoring whether any of said groups of light emitting diodes havebecome incapable of being energized, and means for communicating whichof said plurality of light emitting diodes can still be energized to thepartitioning means.

[0071] In one aspect the light emitting diode lighting device mayfurther comprise:

[0072] a dirt detection means being configured to detect the amount ofdirt on the outer surface of the lighting device and communicating thisamount to the calculation means so that the calculation means maycompensate for the dirt by increasing the light provided by the lightingdevice.

[0073] In one aspect the light emitting diode lighting device mayfurther comprise:

[0074] network connection means for connecting to a network, saidnetwork connection means being configured to communicate with a hostcomputer and the central control unit such that the host computer mayalter said required amount of light.

[0075] In one aspect the light emitting diode lighting device mayfurther comprise:

[0076] a light emitting diode status monitoring system having means formonitoring whether any of said groups of light emitting diodes havebecome incapable of being energized, and means for communicating whichof said plurality of light emitting diodes can still be energized to thepartitioning means;

[0077] a dirt detection means being configured to detect the amount ofdirt on the outer surface of the lighting device and communicating thisamount to the calculation means so that the calculation means maycompensate for the dirt by increasing the light provided by the lightingdevice;

[0078] network connection means for connecting to a network, saidnetwork connection means being configured to communicate with a hostcomputer and the central control unit such that the host computer mayalter said required amount of light; and

[0079] a status indicator means connected to said luminosity measuringsystem, said dirt detection means, and said network connection meanssuch that if the measured luminosity falls beneath a predefined amount,the amount of dirt on the outer surface goes above a certain amount, orif the network connection means is unable to communicate with the hostcomputer then the status indicator means will turn on a signal.

[0080] It is to be understood herein, that if a “range” or “group ofsubstances” is mentioned with respect to a particular characteristic(e.g. angles, wavelengths and the like) of the present invention, thepresent invention relates to and explicitly incorporates herein each andevery specific member and combination of sub-ranges or sub-groupstherein whatsoever. Thus, any specified range or group is to beunderstood as a shorthand way of referring to each and every member of arange or group individually as well as each and every possiblesub-ranges or sub-groups encompassed therein; and similarly with respectto any sub-ranges or sub-groups therein. Thus, for example,

[0081] with respect to angles from 5 to 15, would include for example5.1, 5.2, 6, 5 to 6, 6 to 7,5 to 7, and so on.

[0082] with respect to wavelengths 0.1 millimeters to 10 nanometerswould include for example 0.09 millimeters, 10.1 nanometers, 10.2nanometers, 100 nanometers to 10 nanometers, 0.1 millimeters to 100nanometers, and so on.

BRIEF DESCRIPTION OF THE DRAWINGS

[0083]FIG. 1 shows an embodiment of lighting device of the inventionmounted on a ceiling.

[0084]FIG. 2 shows the configuration of two LED arrays in the lightingdevice of FIG. 1.

[0085]FIG. 2A shows the lighting device using the LED arrays of FIG. 2mounted on a ceiling in a tunnel.

[0086]FIG. 3 show a side view of an LED array of FIG. 2, having a heatdissipation means.

[0087]FIG. 4 shows a diagram of the different parts of the lightingdevice shown in FIG. 1.

[0088]FIG. 5 shows a flow chart of the logic of the microprocessor shownin FIG. 4.

[0089]FIG. 6 shows a perspective front view of the lighting device shownin FIG. 1, with dirt detection sensors showing.

[0090]FIG. 7 shows a side view of the lighting device shown in FIG. 6,with the casing removed.

[0091]FIG. 8 shows a diagram of one example embodiment of a LED statusmonitoring system for use with the lighting device of the invention.

[0092]FIG. 9 shows a diagram of another example embodiment of a LEDstatus monitoring system for use with the lighting device of theinvention.

[0093]FIG. 10 shows a diagram of one possible network structure formultiple lighting devices.

[0094]FIG. 11 shows a diagram of another possible network structure fora great number of lighting devices.

[0095]FIG. 12 shows a diagram of a lighting area, e.g. a tunnel dividedinto several zones.

[0096]FIG. 13 shows a flow diagram of the logic of the host computer ofthe network of lighting devices.

[0097]FIG. 14A shows a top view of a tunnel mounted with severallighting devices of the invention

[0098]FIG. 14B is a cross-section of the tunnel shown in FIG. 14A alongline 14-14, showing the ideal lighting profile of a lighting device.

[0099]FIG. 15A shows a side view of the projection angle of an LEDhaving a symmetrical projection cone.

[0100]FIG. 15B shows a diagram of the projection pattern of the LED ofFIG. 15A.

[0101]FIG. 16A shows a front and a side view of the projection angle ofan LED having a oval projection cone.

[0102]FIG. 16B shows a diagram of the projection pattern of the LED ofFIG. 16A.

[0103]FIG. 17B shows a side view of the composite projection angle oftwo LEDs according to one embodiment of the invention.

[0104]FIG. 17B shows a diagram of the projection pattern of the LEDs ofFIG. 17A.

DETAILED DESCRIPTION

[0105]FIG. 1 shows a lighting device 1 of the invention, having alighting device casing 2 with a transparent face 3 in front of a LEDarray 10. To ensure long-term reliability the casing 2 isenvironmentally sealed, so that dust and water cannot penetrate inside.

[0106] The casing 2 has a shape such that when the lighting device 1 isinstalled in its normal position (e.g. on the ceiling of a tunnel facingdownwards), its light emission axis 4 is tilted by an angle 5 from thevertical axis 6, towards the incoming traffic. This angle 5 can rangefrom −90 to +90 degrees (e.g. 0 to 80 degrees). Light distributionsimulations show that having the angle 5 in the range of 60 to 70degrees allows for optimization of the illuminance. It should of coursebe noted that any sufficient angle may be used.

[0107] In the embodiment of the invention shown in FIG. 2, the lightingdevice 1 has as its main illumination source of an array of individualLEDs 10. The LEDs 10 are assembled on one or more printed circuit boardsections 20, such that the LEDs 10 are perpendicular to the surface ofsaid circuit board sections 20. The number and type of LEDs per sectioncan vary, according to the luminance level required of the lightingdevice.

[0108] As an example, a circuit board section can contain 780 LEDs,arranged in a rectangular array of 26×30 LEDs. The lighting device 1would contain one or more such circuit board sections 20.

[0109] As can be seen in FIG. 2, the circuit board sections 20 areangled with respect to each other. The result is that the light emissionaxes of the circuit board sections 20 are slightly out of sync with theordinary light emission axis 4, for example from 2.5 to 7.5 degrees,though other suitable angles can be used. FIG. 2A shows the lightingdevice mounted on a ceiling in a tunnel. The angling of the circuitboards allows for the lighting device to conform to specific lightinguniformity standards. And is described in greater detail below.

[0110] Some lighting installation standards require specific illuminancelevels over the lighted areas, with a lighting uniformity that mustremain within certain bounds. Lighting uniformity is usually specifiedusing the minimum illuminance over the lighted area (herein referred toas Min), the maximum illuminance (herein referred to as Max), and theaverage illuminance (herein referred to as Mid). As an example,specifications for tunnel lighting typically require a ratio of Min/Maxabove 30%, together with a ratio of Min/Mid 50%.

[0111] It has been determined that for tunnel lighting a way to meet therequirements is to use a series of identical lighting devices 1 in acounter beam orientation 290 at regular spacing (herein referred to asD_(device) 292), as illustrated in FIG. 14A. The experiments have shownthat ideally each lighting device should have a lighting pattern with alateral light projection angle A_(lateral) (herein designated with thereference number 294) wider than the vertical projection angleA_(vertical) (herein designated with the reference number 296), i.e. arectangular-shaped intensity profile 298, as shown in FIG. 14B. FIG. 14Bshows the iso curve of an idealized equal lighting intensity boundary,as seen in a cross-section plane perpendicular to the tunnel main axis.FIG. 14A also shows the direction of traffic by arrow 300.

[0112] The lighting device of the invention in this embodiment seeks tomeet the specifications for public lighting installations using theabove described method. It should also be noted that while targeted tothis approach, other embodiments could be conceived in which differentapproaches are used to satisfy the specifications for public lightinginstallations.

[0113] The most simple way to match the rectangular light projectionpattern 298 with a LED lighting device is to use normal LEDs havingsymmetrical lateral and vertical projection angles A_(lateral) 294 andA_(vertical) 296 equal to the wider of the required angles (i.e.A_(lateral)), the LEDs being installed on a printed circuit boardoriented such that the light projection axis is aligned with thelighting device light emission axis 4. FIG. 15A illustrates thissymmetrical approach. The projection pattern for the symmetrical methodcan be seen in FIG. 15B, which shows the circular projection pattern 302of the approach, with the idealized projection pattern 298. As can beseen some light is wasted in the upper and lower vertical areas 304 ofthe circular projection pattern.

[0114]FIGS. 16A and 16B show another way to obtain a better match to theidealized pattern 298, using special LEDs with an oval intensityprofile. FIG. 16A shows the projection angles of the oval LEDs. ClearlyA_(lateral) 294 is wider than A_(vertical) 296. FIG. 16B shows theprojection pattern for the oval LEDs of FIG. 16A. As can be seen, theoval projection pattern 306 is much closer to the idealized projectionpattern 21.

[0115] Oval LEDs are available on the market but the choice ofanamorphic ratio (A_(lateral)/A_(vertical)) is too limited and theavailable intensity profiles do not lead to optimal results. LEDmanufacturers can develop custom intensity profiles but the cost wouldbe prohibitive.

[0116] Another way to obtain a similar pattern is to use normal LEDswith smaller projection angles and to add special diffusion opticaldevices (such as lenses or holographic filters) to stretch the intensityprofile into an oval shape similar to that shown in FIG. 16B. Thedrawback of this method is increased complexity and costs.

[0117] As can be seen none of the above patterns are really desirabledue to increased cost and wasted light. The present invention thereforeproposes still another approach that is more simple, flexible andcost-effective. Simulations and experiments show that the requiredprojection pattern can be obtained using normal LEDs with a symmetricalprojection angle close to A_(vertical) and installing them on multipleprinted circuit board sections with a slight angular tilt between eachsection so as to stretch the lateral projection angle A_(lateral).

[0118]FIG. 17A shows such an arrangement, with 2 LED 10 having aprojection angle “beta” (herein designated with the reference number308) being disposed on circuit board sections 20. The circuit boardsections 20 are tilted such that the LEDs are disposed at an angle“Alpha” (herein designated with the reference number 310) to each other.FIG. 17B shows the resulting “peanut-shaped” intensity profile 312. Ascan be seen for the figure a very close match to the idealizedrectangular pattern 298 can be achieved using the peanut-shapedintensity profile 312.

[0119] The angles “Alpha” and “Beta” are to be selected, for example, tomatch the road width, the uniformity photometric ratios to bemaintained, the distance between each lighting device and finally by thetilt angle of the lighting device. The number of LEDs required by eachlighting device is determined by the overall illuminance requirement.

[0120] As an example, a simulation for lighting devices made of 780 LEDsdistributed on two printed circuit boards at a tilt angle “alpha” of 10degrees, each having 390 LEDs with a projection angle “beta” of 17degrees. Calculations showed that one lighting device per spacingD_(device)=2 meters was required in order to obtain the requiredilluminance for a typical tunnel. This approach yielded good uniformityvalues Min/Max=50% and Min/Mid=75%. Results have shown that in thisapplication the optimal value for the angle alpha will typically bebetween 5 and 15 degrees. It should be noted that other less optimalangles can be used.

[0121] The resulting approach is very flexible because it uses standardLEDs currently available on the market without any special requirementon the intensity profile. The solution is therefore not limited by oneLED manufacturer's custom design. New lighting devices can also beupdated easily by developments in LED industry: if more candelas isavailable per LED in standard LEDs, the approach can get the benefit ofthe improvement without major redesign of the lighting devices.

[0122] Moving on to FIG. 3, which shows a heat dissipation means 30 foruse with the lighting device 1. The heat dissipation means in thisembodiment comprises a heat conductive compound 40, and a heat sink 50.The heat generated by the LEDs is transmitted through the heatconductive compound 40 to the heat sink 50, which dissipates it.

[0123] The heat dissipation means 30 is included with the lightingdevice 1 since LED output gradually decreases with usage time. As anexample, a typical LED will see its light output decrease by 25% after100,000 hours. The rate of this degradation increases as the junctiontemperature of the LED increases. As an example, a typical LED will seethe same degradation in 140,000 hours at 25_C. as in 110,000 hours at60_C. It is therefore important to keep the junction temperature of theLED as low as possible, in order to increase its life expectancy.

[0124] Most of the heat generated by a LED 10 is dissipated through itsleads 11. In the lighting device 1 the junction temperature of the LEDs10 is minimized by the inclusion of heat dissipation means 30. Thecurrent invention proposes to minimize the LED junction temperature bymaximizing the transfer of heat through the LED leads. This may beachieved as follows:

[0125] First the LED leads 11 are cut so that they stick out of theprinted circuit boards 20 to a certain length. Second the space betweenthe LED leads is filled with the compound 40 which is conductive to heatbut not to electrical current. And example of an appropriate compoundwould be a thermally conductive silicone paste. The compound 40 willcover the whole surface of the printed circuit board on the oppositeside of the LEDs. The thickness of the compound 40 should be slightlygreater than the length of the LED leads 11 so that no leads 11 extendout of the compound 40. Finally a metallic heat sink 50 is applied incontact with the compound 40, to dissipate the heat transferred from theleads 11 through the compound 40. This heat sink 50 can alternately beintegrated with the body of the lighting device casing 2.

[0126] In an alternate method the LED leads 11 can be cut so that theydo not protrude from the printed circuit boards 20. A thermallyconductive soft elastomer sheet would then be placed between the printedcircuit board 20 and the heat sink 50. And example of this kind of sheetis made by the manufacturer Thermagon.

[0127]FIG. 4. shows an electronic diagram of the lighting device 1 shownin FIG. 1. FIG. 4 shows that the LEDs 10 are grouped in a plurality ofgroups of LEDs 60. An example design could have for instance 78 groupsof 10 LEDs each.

[0128] Connected to each groups is a constant current source 70 whichcan turn the group either on or off. The constant current sources 70 areconnected to a microprocessor 80. The microprocessor 80 is set tocontrol the lighting device, and is in this embodiment of the inventiona controller means. In the case of the current sources 70 themicroprocessor 80 has an energizing means which controls which of thecurrent sources 70 are turned on and which are turned off, therebycontrolling each of the groups of LEDs 60. The energizing meanscomprises in this embodiment a suitably programmed computer method forthe microprocessor 80. This suitable programming meaning being capableof taking as its input two lists of LED groups, one list containing theLED groups which are to be turned on and one list containing the LEDgroups which are to be turned off. The suitable programming furtherbeing capable of signalling each of said current sources 70 to eitheractivate or de-activate based on said lists.

[0129] The group structure of the LEDs is desirable because it allowsgreat control of the LEDs while not taking up as much circuitry asindividual control of each individual LED. Furthermore the groupstructure is very flexible in allowing for variable dimming of theluminosity level of the lighting device. The luminosity level will beadjustable by controlling the number of LED groups turned On or Off.

[0130] In the example design containing 78 individual LEDs groups perprinted circuit board, the luminosity will be adjustable with aresolution of 100/78=1.28%. As can be seen the groups structure methodof dimming allows for great flexibility in dimming and further allowsthe LED groups to use only a single current level thus simplifies thecircuitry of the lighting device.

[0131] Additionally, to prevent power transients when the tunnellighting is turned On or Off, or when its dimming level is changed themicroprocessor in each lighting device will automatically make anyluminosity transition gradual. This is achieved by turning LEDs group Onor Off one by one, with a slight time delay between each group.

[0132] While in this embodiment the current source 70 is a constantcurrent source, it could also be a variable current source. A variablecurrent source has certain advantages in that it could be used toimplement a long term LED degradation compensation system in which thecurrent source could supply more power to compensate for lower output bythe LEDs over time.

[0133] Also connected to the groups 60 is a LEDs status monitoringsystem 90 which monitors the current flowing through the LEDs groups 60in order to identify any defective LED groups.

[0134] The lighting device further includes a luminosity measuringsystem 100 which will measure the luminosity of one or more test LEDs101, in order to regulate the luminosity output of the lighting device.

[0135] The system in this aspect also includes status indicator means110 which has a light that is visible from the outside of the lightingdevice. The status indicator 110 will be activated by the microprocessorwhen the lighting device requires servicing. The status indicator 110normally has two modes, but can be extended to allow for further modes.The normal modes are NORMAL in which the light is off and the lightingdevice is functioning normally. The second mode is END OF LIFE in whichthe light is turned on. In this mode the lighting device has detectsthat the LEDs have degraded beyond a predetermined cutoff point. In theembodiment of the lighting device shown in FIG. 4, the status indicatorhas two further modes. These first of these modes is CLEANING NEEDED inwhich the light is set to slowly flash. In this mode the lighting devicehas detected that the transparent face of the casing has become toofilthy and that the lighting device requires cleaning. The final mode isNO CONNECTION in which the light is set to quickly flash. In this modethe lighting device has detected that it has lost its connection to anetwork and a host computer. The status indicator, its modes, and howeach mode is detected will be explained in greater detail below.

[0136] The lighting device also includes network connection means 120,for connecting the lighting device to a network 130. Through the networka host computer can monitor the status of the lighting device, and setthe luminosity output of the lighting device. The lighting device canalso include an address setting switch 135 which can be access from theoutside of the lighting device, either manually of through a remotesignal. When the address setting switch 135 is activated a signal issent through the microprocessor 80 to the network connection means 120.The network connection means then contacts the host computer through thenetwork and request a network address for the lighting device.

[0137] Finally, the lighting device contains a non-volatile memory 140,which can be used to store various information which the microprocessor80 needs to perform its function. Such information can include thelighting devices network address, the luminosity of a standard LED, andthe current luminosity setting of the lighting device.

[0138] The microprocessor 80 shown in FIG. 4, implements several usefulfunctions for the lighting device. In addition to the energizing meanswhich aids in the variable dimming capacity and control of the LEDgroups, the microprocessor 80 has several means which allows thelighting device to compensate for long-term luminosity degradation.These means are timer means which is a software method which keeps trackof time, calculation means which is a software method capable ofcalculating the number of LED groups which are needed to provide therequired light, and partitioning means which is a software method forselecting which LED groups to turn on. Each of these means will bedescribed in greater detail below.

[0139] One main long-term luminosity degradation compensation of thesystem may be based providing more groups of LEDs than are require atthe start of the life cycle of the lighting device. The number of LEDsrequired to generate the specified luminosity of the lighting device atthe start of its life-cycle can be determined using the initial LEDspecifications. It is known that as the LEDs age, their outputluminosity will gradually decrease, or equivalently more LEDs will berequired to achieve the specified luminosity. The lighting device maytherefore be designed with a number of extra LED groups which aresufficient to maintain its specified luminosity up to the end of itslife-cycle. The number of extra groups of LEDs varies, and thecalculation of this number will be explained in greater detail below.

[0140] At certain intervals in the life-cycle of the lighting device,the timer means of the microprocessor causes the calculation means tocalculate the number of necessary LED groups. This calculation is basedon an idealized LED luminosity which it obtains from the luminositymeasuring system 100, as shown in FIG. 4. As the luminosity of the testLEDs of the luminosity measuring system 100 degrade the calculationmeans will turn on more of the extra LEDs groups to maintain theluminosity of the lighting device. Which of the groups to turn on isselected by the partitioning means, which follows an algorithm whichwill be described in greater detail below.

[0141] The number of extra LED groups may be estimated as follows:

[0142] Estimation of the Number of Extra LED Groups

[0143] The LED Array of the lighting device is designed with a number ofextra LEDs groups sufficient to maintain its specified luminosity up tothe end of its life-cycle. The life-cycle of the lighting device ispredetermined and may be for instance between 10 and 15 years. The extraLEDs groups will gradually be used as the lighting device ages.

[0144] The number of extra groups is determined as follows, using thisset of definitions:

[0145] L_(tot)=Total Luminosity of the lighting device

[0146] N_(on)(t)=Number of groups turned On (as a function of time) tomaintain constant L_(tot)

[0147] L_(led)(t)=Luminosity (as a function of usage time) for a typicalLED

[0148] t_(elc)=End-of-Life-Cycle time

[0149] n_(led)=Number of LEDs per group

[0150] N_(start)=Number of LED groups needed at life-cycle startup (t=0)

[0151] N_(extra)=Number of extra groups needed to maintain TotalLuminosity L_(tot) at End-of-Life-Cycle time t_(elc)

[0152] N_(group)=Total number of groups in lighting device

[0153] At any given time, the microprocessor monitors L_(led)(t) throughthe monitor LEDs. It then adjusts the number N_(on)(t) of groups turnedOn so that the Total Luminosity L_(tot) of the lighting device remainsconstant, according to the following relation:

L _(tot) =N _(on)(t)*n _(led) *L _(led)(t)  (1)

[0154] From which is obtained:

N _(on)(t)=L _(tot) /{n _(led) *L _(led)(t)}  (2)

[0155] At start of life-cycle (t=0):

N _(start) =N _(on)(0)=L _(tot) /{n _(led) *L _(led)(0)}  (3)

[0156] where L_(led)(0) is the start-up LED luminosity.

[0157] N_(on)(t) will gradually increase as L_(led) decreases with LEDage. The total number N_(group) of LED groups in the lighting devicemust be high enough to satisfy (2) at the End-of-Life-Cycle time, whenLED luminosity will be at its minimum:

N _(group) =N _(on)(t _(elc))  (4)

[0158] After combining (2) and (4):

N _(group) =N _(on)(t _(elc))=L_(tot) /{n _(led) *L _(led)(t_(elc))}  (5)

[0159] Since by definition:

N _(extra) =N _(group) −N _(start)  (6)

[0160] (3), (5) and (6) can be combined to obtain:

N _(extra) =L _(tot) /{n _(led) *L _(led)(t _(elc))}−L _(tot) /{n _(led)*L _(led)(0)}  (7)

[0161] The End-of-Life-Cycle luminosity L_(led)(t_(elc)) can be obtainedfrom the LED manufacturer's specifications sheet. This value is alsodependent on ambient temperature and LED junction current, so thesefactors must be taken into account when evaluating the number N_(extra)of extra LED groups for the lighting device.

[0162] Equation (7) is in fact a worst-case approximation of N_(extra),because by using L_(led)(t_(elc)) as the End-of-Life-Cycle LEDluminosity it is assumed that the LEDs are always On during the fulllife-cycle of the lighting device. This is in practice not the casebecause in the early life of the lighting device, only N_(start) groupsout of the total N_(group) are On. This means that on average the LEDsdegrade less rapidly than estimated with (5).

[0163] The average degradation of each LED may be further improved by anautomatic LED usage equalization mechanism implemented in the lightingdevice. In this mechanism, the microprocessor continuously performs arotation of the LED groups turned On. This rotation is kept slow enough(e.g. once per hour) so as not to be noticeable by casual observers. Inthis way, even if not all groups out of the total available N_(group)are required during the lighting device's early life, all N_(group)groups are still exercised equally on average and therefore degradeequally in the long term. The automatic LED usage equalization mechanismwill be explained in greater detail later.

[0164] Taking this mechanism into account, a new reduced value for thenumber of extra groups N_(extra) (herein referred to as Nauto_(extra))is obtained. This involves an integration of the LED luminosityL_(led)(t) over the averaged actual LED On time during the completelighting device life-cycle. Typically Nauto_(extra) can be reduced by afactor of 20% to 50% over the value N_(extra) given by (7), depending onthe specific Luminosity curve L_(led)(t) of the LEDs during the lightingdevice life-cycle.

[0165] Example of Values Obtained for a Typical Lighting Device

[0166] Below are shown example values obtained for a lighting deviceusing typical Amber-colored InGaAIP LEDs.

[0167] The following is assumed:

[0168] L_(tot)=1500 cd (candelas) total lighting device luminosity

[0169] n_(led)=10 LEDs per group

[0170] t_(elc)=10 years End-of-Life-Cycle time

[0171] T_(ambient)=25° C. ambient temperature

[0172] I_(junction)=20 mA (milliAmperes) LED junction current

[0173] The LED manufacturer specifies:

[0174] L_(led) at start-up time (t=0)=3.5 cd (candelas)

[0175] L_(led) at End-of-Life-Cycle (t=10 years)=55% of L_(led)(0)=1.92cd

[0176] According to (3):

[0177] N_(start)=L_(tot)/{n_(led)*L_(led)(0)}=1500/(10*3.5)=43 LEDgroups needed at start-up.

[0178] According to (5):

[0179] N_(group)=L_(tot)/{n_(led)*L_(led)(10 y)}=1500/(10*1.92)=78LEDgroups needed at End-of-Life

[0180] Therefore, according to (6):

[0181] N_(extra)=N_(group)−N_(start)=78−43=35 extra LED groups tocompensate for LED degradation

[0182] Taking into account the Automatic LED Usage Equalizationmechanism:

[0183] Nauto_(extra)=25 extra LED groups, or a reduction of about 28%over N_(extra)

[0184] For the long term degradation compensation of the lighting deviceto be effective it is important that the calculation means has anaccurate idea of the current luminosity output of the LED groups.Therefore, in addition to the LED groups, this system will use one (ormore) test LED 101 opto-coupled to a light intensity-measuring device102, as shown in FIG. 4. The light intensity measuring devices 102 canbe for instance photodiodes or any appropriate light sensor. Whendesired the light intensity-measuring devices 102 can measure theluminosity output of the test LEDs 101, and obtain a standard luminosityfor the LEDs of the lighting device.

[0185] The test LEDs 101 will be identical to the LEDs used in thegroups, supplied with the same constant current, kept at the sametemperature as the group LEDs, and turned On and Off in such a way as tomaintain or reflect the same or analogous long-term usage rate as thegroup LEDs, as described below.

[0186] As will be described in details later, the lighting device has acontroller means to count and store the cumulative usage time duringwhich each LED group is activated, and further implements an AutomaticLED Usage Equalization mechanism to ensure that on average all LEDgroups are used for the same cumulative time. The same controller meansalso counts and stores the cumulative usage time of the test LEDs, andat regular intervals automatically activates the test LEDs long enoughto ensure that their cumulative usage time is equal to that of the groupLEDs.

[0187] For example the controller means could activate test LEDs everytime the average cumulative usage time of the lighting LEDs exceeds thecumulative usage time of the test LEDs, and turn the test LEDs off everytime the cumulative usage time of the test LEDs is greater than or equalto the cumulative usage time of the lighting LEDs.

[0188] The light intensity-measuring device 102 coupled to the test LEDs101 is read by the controller means. By comparing the test intensity toa reference value, the calculation means can estimate the LED luminosityvariations at any given moment and compensate by adjusting the number ofLEDs groups turned ON, thereby regularizing the overall lighting deviceluminosity.

[0189] The comparison to the reference values can be seen in FIG. 5,reference number 180. The test intensities L1 and L2 are measured in 176and 178. These values are then compared to reference values Lr1 and Lr2which are set during the calibration of the lighting device (154, 156,158). The LED degradation factor F1 is calculated using the followingformula F1=((L1/Lr1)+(L2/Lr2))/2. As can be seen from the formula theLED degradation factor is averaged over the test diodes such that in thecase of abnormal behaviour in one test LED the results will not becompletely skewed.

[0190] Number of Test LEDs Provided with a Typical Lighting Device

[0191] It is preferable to have more than one Test LED, in case the TestLED fails or has abnormal degradation behavior. The probability of theseoccurrences simultaneously to more than one LED is proportionallysmaller.

[0192] Since LEDs have a typical MTBF (Mean Time Before Failure) in themillions of hours, the probability of these occurrences for one LED isalready very low during the lighting device life cycle. Therefore using2 test LEDs is considered sufficient to obtain a very reliable system.

[0193] The number of test LEDs is not related to the number of lightingLEDs in the lighting device: the test LEDs' behavior is independent ofthe number of lighting LEDs.

[0194] Separate Test LEDs

[0195] In order to provide an accurate picture of the lighting device'slighting LEDs state, the test LEDs must operate under identicalconditions: same junction current, same temperature, same usage time.

[0196] The most direct way to accomplish this is simply to use some ofthe lighting LEDs as test LEDs. However this has the followingdrawbacks:

[0197] Each test LED must be optically coupled to a lightintensity-measuring device, such as a semiconductor photo-sensor.Furthermore, no outside light must filter in this coupling, so that theintensity measurement accurately reflects the Test LED intensity. Such acoupling+photo-sensor assembly can take a substantial amount of physicalspace in front of the Test LED (typically at least one inch). Using alighting device's lighting LED as Test LED would require to provide thisspace between the whole LEDs PC-Board and the lighting device'stransparent display window, therefore substantially increasing theoverall lighting device's dimension.

[0198] Because of the automatic LED usage equalization mechanism, thelighting LEDs groups are turned On and Off in an unpredictable way asthe lighting device ages and the LED groups' usage goes through arotation. It can therefore be impractical to wait until a particularlighting LED used as Test LED is turned On by this mechanism in order tobe able to make an intensity measurement.

[0199] Lighting LEDs are organized in groups of typically 10 LEDs. If asingle LED out of a group fails and becomes open-circuited, the wholegroup fails. This means that the MTBF of a complete group issubstantially smaller than the MTBF of each LED. Using a lighting LED asTest LED is therefore less reliable than using an individually connectedTest LED.

[0200] To overcome these issues separate test LEDs driven withindividual current sources can be used. In order to obtain an accurateoperation, the following precautions are taken:

[0201] Test LEDs are driven with the same junction current as thelighting LEDs.

[0202] Thermal modeling inside the lighting device shows that theambient temperature is quite equalized throughout the lighting device.Therefore the test LED ambient temperature is close to or the same asthat of the lighting LEDs.

[0203] The microprocessor implementing the automatic LED usageequalization mechanism simultaneously turns the test LEDs On and Off sothat they maintain an averaged usage time equal to that of the lightingLEDs. Because they are independent from the lighting LEDs, the test LEDscan be turned On whenever intensity measurements are required.

[0204] These precautions ensure that the test LEDs will degrade in thesame way as the lighting LEDs.

[0205] Automatic LED Usage Equalization

[0206] At each stage in the course of the lighting device life, avariable number of LEDs groups will be On or Off, according to thedimming level requested and the luminosity compensation mechanism. Thememory means 140 shown in FIG. 4, will keep count of the usage time ofeach of the LEDs group in the LED Array, and store these individualusage time values.

[0207] When selecting which LEDs groups to turn On at any given time,the partitioning means will automatically prioritize the use of LEDsgroups having the shortest usage time. This prioritization is achievedby programming the partitioning means to follow the following algorithm:

[0208] sort the LED groups by usage time;

[0209] selecting the appropriate number of groups with the least amountof usage time.

[0210] This prioritization will ensure that all LEDs have an equalizedusage time with no LED degrading faster than others, thereforeoptimizing the long-term luminosity degradation and stability of thelighting device.

[0211] The interconnections of the timer means, calculation means,luminosity measuring system, and the partitioning means can be seen ingreater detail in FIG. 5, which shows flow of logic in themicroprocessor 80 shown in FIG. 4.

[0212] After boot initialization 150 the microprocessor waits.Periodically it checks whether a communication has been received fromthe network. The lighting device can receive three kinds ofcommunications, a calibration command 154, mainly used during factorystart-up, which causes reference values for luminosity degradationcalculation to be set; a set intensity command 160 which causes thelight intensity output of the lighting device to be set to a new value162; and a send status command 164 in which the lighting device isrequested to send its status to the host computer. The status of thelighting device includes all pertinent information, comprising currentluminosity setting, current actual luminosity output, current LEDdegradation factor, current dirt accumulation factor, current number ofLED groups in use, current number of open-circuited LED groups andcurrent average usage time of LED groups. For definitions of thesefactors and numbers please see below.

[0213] If no communication has been received by the lighting device fora predetermined time then the lighting device assumes that its link tothe network 130 has been lost and sets the status indicator 110 (seeFIG. 4), to the NO COMMUNICATION mode.

[0214] Finally the microprocessor, periodically recalculates the numberof active groups in the lighting device and rotates the active groups.Seen in FIG. 5, this happens when the microprocessor checks the timermeans in 174. If a certain interval has elapsed, the luminositymeasuring system as seen in FIG. 4, is activated and new luminosityreadings are taken, and the percentage of LED degradation factor iscalculated (176, 178, 180). This new LED degradation factor is checkedagainst a preset value (for instance 55%) to see if the lighting devicehas reached its end of life. If yes then the status indicator 110 (seeFIG. 4), is set to the END OF LIFE mode.

[0215] At this point an optional dirt detection means may be called intouse. Turning to FIGS. 6 and 7, which show the dirt detection meanscomprising of a plurality of light sensors 200, disposed inside thelighting device 1. The dirt detection means functions as follows:

[0216] The lighting device's light source sends out light outside thelighting device through the transparent face 3. When the transparentface 3 is clean, there is hardly any light reflection inside thelighting device. On the other hand, as the dirt level increases, so doesthe light reflection level. Therefore, the light sensors 200 willmeasure the light level reflected inside the lighting device, determinethe dirt level, compare both results with preprogrammed data in themicroprocessor, and, if required, trigger an alarm informing thelighting device network operator of the current status.

[0217] In an alternate embodiment the sensors 200 can be set to detectelectromagnetic radiation corresponding to a wavelength from 0.1millimeters to 10 nanometers (i.e. Infrared, visible, and ultravioletlight). The sensors would in this embodiment of course be coupled withlight emitting diodes which emit electromagnetic radiation of theappropriate wavelength.

[0218] For example, in one embodiment infrared emitters coupled withinfrared sensors (e.g. at 940 nm) may be used. The infrared sensor maybe chosen with a bandwidth low enough to reject the visible light comingfrom the lighting LEDs of the lighting device. This is to ensure thatthe dirt measurements remain independent of the lighting LEDs output,which can vary over time in unpredictable ways due to varying luminositysettings as set by the network host computer, as well as due to the LEDUsage Time Equalization mechanism which constantly varies the activationof LED groups.

[0219] Turning back to FIG. 5, which shows the dirt detection systembeing called upon and providing a dust masking factor Fd to be measured.If the dust masking factor Fd is under a preset number (in this case75%) the status indicator 110 (see FIG. 4), is set to CLEANING NEEDEDmode.

[0220] After the luminosity measuring system and the dirt detectionmeans are finished the calculation means is activated to calculate thenumber of groups which are required to provide sufficient light based onthe set luminosity, and the amount of LED degradation, and the dirt onthe transparent face.

[0221] The formula used for this calculation is X=(Nstart*I)/(F1*Fd). Inthe formula X is the number of groups required to provide the luminositywhich is desired. Nstart is the total number of LED groups used at thestart of the lighting device's life-cycle. I is the luminosity settingof the lighting device, with 0 being no light and 1 being maximumlighting. F1 is the LED degradation factor, with 1 being no degradationand lower values indicating LED degradation. E.g. a value of 0.5 wouldindicate that the LEDs are only giving off half of their originalluminosity. Finally, Fd is the percentage of light going through thelighting device's transparent face, with 1 being full transmissivity andlower values indicating light lost due to dirt. E.g. a value of 0.5would indicate that only half of the light is going through thetransparent face of the lighting device.

[0222] After the calculation means calculated X, the partitioning meansis activated (194, 196). The partitioning means sorts all the LED groupsby usage time, and then selects the X groups with the least amount ofusage time. These X groups with the least amount of usage time are thenassigned to a first energized groups, while the remaining LED groups areassigned to a second non-energized group. The energizing means is thencalled on to energize the members of said first energized group and tode-energize the members of said second non-energized group.

[0223]FIGS. 8 and 9 show in more detail the LEDs status monitoringsystem 90. The system 90 monitor on-demand the LEDs integrity bymeasuring whether any LEDs groups are open-circuited. A simple way toachieve this function is shown in FIG. 8, and functions by the followingprocess:

[0224] Turn Off all LED groups.

[0225] At the common supply point of all LED groups, install in serieswith the supply line a test optocoupler 210.

[0226] Turn On one LEDs group; if it functions normally, the current itdraws will turn On the test optocoupler 210. If one or more LED in thegroup is open-circuited, the group will draw no current and thereforethe test optocoupler will remain Off. The test optocoupler output ismonitored by a microprocessor input.

[0227] Successively turn On each of the LEDs groups in the LEDs Arrayand monitor them.

[0228] Once the test is finished, remove the test optocoupler from thesupply line and resume normal operation.

[0229] Another way of accomplishing the LED status monitoring system isby continuous monitoring. In this version, shown in FIG. 9, the systemis accomplished by adding current sensing inputs 220 on each LED groups,and multiplexing them to the lighting device's microprocessor. Thismethod allows for monitoring the LED groups' status without interruptingthe lighting device's normal operation, at the cost of substantiallymore circuitry.

[0230] Testing Procedure Activation

[0231] The LED status monitoring system with the first method requiresan interruption of the lighting device's normal operation. During themeasuring process, all groups are turned Off and each is then turned Onone by one while its current is measured by the lighting device'smicroprocessor; open groups will report zero current. The time requiredto perform the measurement will typically be around 10 ms per LED group;therefore for a typical lighting device with 78 LED groups the completetesting procedure will take around 1s.

[0232] Because this testing procedure will be visible from outside (thelighting device will stop functioning normally during a second or so,and display a moving light pattern as each LED group is activated one byone), it cannot be performed too often. It will typically be performedonce per 24 hours.

[0233] The testing procedure can be triggered in two ways:

[0234] 1. The lighting device's microprocessor can perform the testingprocedure on its own, through a built-in timer with a programmableperiod. Each lighting device contain a timer counter, automaticallysynchronized to the same time-of-day by the network host computer sothat all lighting devices in the network have a synchronized time base.

[0235] 2. Upon receiving a specific command from the network hostcomputer.

[0236] In both cases, it is preferable to stagger the testing procedurefor each lighting device in the network, so that normal operation isinterrupted for only one (or a few) lighting device(s) at a time. Inthis way all lighting devices in the network can eventually be monitoredwithout compromising the lighting level provided by the whole system.

[0237] The status indicator 110 as seen in FIG. 4, is a light which isvisible from the outside of the casing 2. Under control of themicroprocessor, the status indicator 110 will provide the followinginformation about the current state of the lighting device: IndicatorState Status Description Off Normal Normal operation Slow FlashingCleaning Needed The transparent face of the lighting device hasaccumulated an excess of dirt Fast Flashing No Communication Thecommunication link with the Host PC is lost On End of Life The lightingdevice can no longer provide its specified luminosity, due to LEDfailure or degradation.

[0238] “Cleaning Needed” Status

[0239] The lighting device's built-in dirt detection sensor hasdetermined that dirt accumulation on the face plate has decreasedluminous intensity by a factor greater than a predetermined thresholdvalue (typically 25%). To make this status clearly visible for a serviceteam on the ground, the Status indicator is flashed at a slow rate.

[0240] “No Communication” Status

[0241] The lighting device expects to receive commands at regularinterval from the network Host PC (typically a few minutes). When thistime-out interval (as measured by the lighting device's built-in timer)is exceeded, the lighting device detects the absence of communicationand reverts to a “Default” condition. This Default condition can includethe following properties:

[0242] 1. Fast Flashing of Status Indicator

[0243] 2. Going to full intensity, to ensure that the worst-caselighting needs are fulfilled.

[0244] “End of Life” Status

[0245] As the lighting device ages and the luminosity of its LEDsdecreases, more and more LED groups are turned On to maintain a constanttotal luminosity. Eventually all available LED groups are required toachieve the full-intensity state. From that time onwards, the lightingdevice full-intensity luminosity will gradually decrease. To indicatethis “End of Life” status, the Status Indicator is turned On by thelighting device's microprocessor.

[0246] This event can be accelerated if some LED groups actually fail(become open-circuited), as detected by the LED status monitoringsystem, since the pool of available LED groups is correspondinglyreduced. Note that at this “End of Life” point the lighting device isstill operational, and may maintain a sizable proportion of itsfull-intensity luminosity for more years. Also, lower luminosity states(as selected by the network Host PC, for example during night time) canstill be completely within specifications, as they may require fewer LEDgroups than the total available.

[0247] In one embodiment of the invention lane use signals may beincluded in the lighting device. In this embodiment each lighting devicewill incorporate a set of diodes (besides the ones being used forlighting purposes) which will serve as lane use signals in order toinform motorists on current road conditions. A red X will indicate thatthe lane is closed. Furthermore, one or many other signals can beincorporated according to prevailing circumstances. A green arrow willindicate that the lane is open, and if motorists have to be instructedto change lane (left or right), a yellow arrow pointing in theappropriate direction can be displayed. These signals can have acontinuous or flashing display and will be controlled by the operator. Acommand is sent by the system operator from the host computer connectedby the network connection means to each lighting device or lightingdevice's controller.

[0248] When a lane use signal is being displayed, the operator can sendanother command from the host computer through the network, to reducethe selected lighting device's brightness to the desired level, in orderto enhance contrast for better visual impact of the signal. This commandfunction is most often used in conjunction with the lane closed signal(the red cross). This is because, since the lane is closed then itrequires less lighting. A moderate level such as for instance 50% of thelighting device's nighttime setting (e.g. 1.25 cd/m²) will usually besufficient to provide adequate lighting.

[0249] A detection and protection mechanism will prevent displaying morethan one signal concurrently on the same lighting device in order toavoid confusion and potentially dangerous situation or motorists. Thedetection and protection mechanism will work in conjunction with the LEDstatus monitoring system 90, and the microprocessor 80 as seen in FIG.4. The LED status monitoring system will be connected to the signal LEDsand to the microprocessor such that the LED status monitoring systemmonitors the signal LEDs and reports to the microprocessor. Themicroprocessor contains means for receiving the status of the signalLEDs from the LED status monitoring system and checking whetherconflicting signals are being displayed.

[0250] An appropriate communication mechanism will return information tothe system operator concerning the current status of the signals beingdisplayed on the network's lighting devices.

[0251] For instance the appropriate information can be appended to thelighting device status report which the host computer will periodicallyrequest from each lighting device. The host computer can then receivethe information and interpret it as necessary.

[0252] One useful part of the lighting device of the invention is thelinking of a number of lighting devices to a network 130, and theircontrol by the host computer through this network. This systems-levelaspect of the invention brings a number of further capabilities andfeatures.

[0253] Any communication network allowing multidrop connection of alarge number of lighting devices to the host computer is suitable. As anexample, the following protocols can be used: RS-485, Ethernet, TCP/IP.

[0254]FIGS. 10 and 11 show example networks of lighting devices. FIG. 10shows an example network topology with only a few lighting devices forinstance less than 128 devices. FIG. 11 on the other hand shows a largernetwork with a large number of lighting devices, for instance greaterthan 128 devices. In this network topology the lighting devices aregrouped into individual nodes of less than 128, and node controllers 235are included to relay information between the host computer and thelighting devices.

[0255] Each lighting device 1 on the network will be assigned andindividual, unique address. The system is designed so that the hostcomputer keeps a record of the physical location of each lightingdevice, referenced by its network address.

[0256] The address of each lighting device is stored in non-volatilememory within its electronic circuit. The lighting device is equippedwith an address setting switch, accessible from the outside of the case,for instance physically or through remote controlling means such asinfrared, laser or Radio Frequency signals. At system installation, thisswitch is activated to signal to the Host PC that the lighting device isrequesting a network address, which is then generated and assignedautomatically to the lighting device by the host computer.

[0257] The network linking of a number of lighting devices with a hostcomputer has the following advantages:

[0258] 1) Using the Host-to-lighting device communication directionallows the host computer to control important global aspects of thelighting system, such as the lighting intensity in specific zones of thesystem as a function of the time-of-day and/or ambient illumination,gradual dimming of lighting intensity in intensity level transitions,and activation of special functions such as integrated lane use signals.

[0259] 2) Using the lighting device-to-Host communication directionallows the transfer of lighting devices status information to the hostcomputer

[0260] These elements are now described in greater details:

[0261] One of the functions of the host computer can control the overallor Global Intensity level of a lighting area. An example of this isshown in FIG. 12, which shows the lighting area (in this case a tunnel)being divided into three zones: A threshold zone 242, a transition zone244, and an interior zone 246.

[0262] Because it has individual control over each lighting device, thehost computer can vary the intensity level for each specific zone of thelighting area. For example, in a typical tunnel the daytime illuminationin the threshold zone 242 will be set at 200 cd/m², the inner zone 246at 5 cd/m², and the transition zone 244 at intermediate intensities.

[0263] The number, size and location of the lighting zones can be easilyand arbitrarily modified through the Host software.

[0264] Another example of variation controlled by the host computer isthe intensity level according to the time of day, and/or the ambientillumination.

[0265] According to standard requirements specified by the IlluminationEngineers Society of North America in their document RP22-96illumination in the interior a tunnel should be at least 5 cd/m² in thedaytime, and 2.5 cd/m² in the nighttime. As the lighting requirementsfor nighttime are substantially smaller than those of daytime, thesystem can reduce energy consumption by lowering the intensity duringthe nighttime.

[0266] To achieve this task the host computer can be equipped with aambient illumination sensor at the entrances to the tunnel. The hostcomputer would then use these sensors to detect ambient illumination.The ambient illumination measurement could then be used to adjust thelight of the tunnel. Typical recommendations call for maintaining thethreshold area illumination at least at {fraction (1/10)}th the level ofthe ambient illumination during daytime.

[0267] When changing from one Intensity level to another, the Host cangenerate gradual Intensity transitions in order to maximize energyefficiency.

[0268] For example, when changing from Night to Day luminance levels, adiscrete control system would have to select the Day level as soon asmorning ambient light starts to grow. Instead, the host computer canperform a gradual ramping between Night and Day levels, thereby delayingthe increased energy consumption of the day level and enhancingdrivers'visual comfort. The ramping can be triggered when the ambientillumination reaches a predetermined level (typically 100 cd/m²) andlast for a user-adjusted length of time (typically 30 minutes).

[0269] Another important function of the host computer is monitoringlighting device status. At certain intervals the host computer will polleach lighting device on the network, to obtain its current statusinformation.

[0270] This information can be tabulated and logged; alarms can betriggered if any potential failure or degradation is detected; andmaintenance reports can be generated, listing the location andidentification of each lighting device requiring servicing.

[0271] To prevent the loss of tunnel illumination under any circumstance(short of power failure), each lighting device will automatically revertto its normal Intensity level whenever contact with the host computer islost for a time interval longer than an adjustable CommunicationTime-Out period. In case of power failure, the system can facilitate thegeneration of emergency lighting backed up by UPS (Uninterruptible PowerSupply). The energy consumption can be reduced to a minimum, either bygreatly dimming the lighting devices, or by dynamically alternating thelighting devices in the On state.

[0272] In order to reduce energy consumption, the host computer candetect the presence of vehicles in the lighting area (through standardVehicle Presence Detectors), and dim the Intensity level when no vehicleis present. This dimming can be further refined on a zone-by-zone basisas the vehicle moves across the lighting area.

[0273] Turning to FIG. 13, which shows the logic of the host computer.After initialization 250, the host computer enters a cycle in which itfirst checks the ambient light intensity and sets the lighting devicesaccordingly (252, 254, 256, 258). Afterwards the intensity setting ofthe lighting devices may be manually overridden (260, 262) if desired bya controller of the system. After the intensity of the lighting deviceshas been set the host computer proceeds to check the status of eachlighting device in the network logging their status or flagging thelighting device as defective if the lighting device fails to respond(264, 266, 268, 270, 272). After each lighting device has been checkedthe host computer evaluates the network to see if sufficient light isbeing provided in the lighting area. If the luminosity if below standardof below a critical level an appropriate message will be displayed tothe controller of the system.

[0274] Summary of the Advantages of the Invention Feature ExplanationSummary of the advantages of the invention. Better light efficiency LEDsare inherently more efficient than current HID luminaries; Opticalsystems further improves the system. Better light uniformity Lightingdevice optical system opti- mized lighting pattern. Since lightuniformity is greater, lower overall lighting levels can be used. Tightintensity regulation and tol- Lighting device luminosity is erance knownand stable throughout its life- cycle, allowing lower overall energydissipation. Proportional dimming Allows the use of the optimal inten-sity required at each moment/loca- tion. Vehicle presence detectionAllows dimming when no vehicle present. Cost saving features. Reducedusage cost: Competitive initial cost Initial cost equivalent to currentHID lighting devices Lower energy costs Higher energy efficiency tocurrent usage optimization Longer life-cycle LED lighting devicelife-cycle esti- mated at 15 years Reduced maintenance cost: Precisestatus monitoring through Precludes the need of regular inspec- hosttions Low voltage operation Allows the use of non-electricians formaintenance Fast on-site identification of defec- Through StatusIndicator tive lamps

1. A lighting device comprising a plurality of groups of light emittingdiodes, each of said groups of light emitting diodes containing one ormore light emitting diodes, each of said light emitting diodes beingconfigured so as to pass between an energized light emitting state and anon-energized state; luminosity measuring means for providing a standardluminosity reading at predetermined time intervals; controller means fortransferring, at predetermined time intervals, in response to saidstandard luminosity reading, one or more of said groups of lightemitting diodes between a first energized group wherein said lightemitting diodes are in said energized light emitting state and a secondnon-energized group wherein said light emitting diodes are in saidnon-energized state.
 2. A lighting device as claimed in claim 1, whereinsaid controller means is configured to maintain all of the lightemitting diodes in said first energized group when a predeterminedluminosity reading is provided by said luminosity measuring means.
 3. Alighting device comprising a plurality of groups of light emittingdiodes, each of said groups of light emitting diodes containing one ormore light emitting diodes, each of said light emitting diodes beingconfigured so as to pass between an energized light emitting state and anon-energized state; usage time measuring means for providing a usagetime measurement for each of said groups of light emitting diodes atpredetermined intervals; controller means for transferring, atpredetermined time intervals, in response to said usage timemeasurements, one or more of said groups of light emitting diodesbetween a first energized group wherein said light emitting diodes arein said energized light emitting state and a second non-energized groupwherein said light emitting diodes are in said non-energized state.
 4. Alighting device as claimed in claim 1, wherein said controller meansfurther comprises: means for detecting whether any of said groups oflight emitting diodes have become unable to pass between said energizedlight emitting state and said non-energized state, and transferring saidgroups to a third non-functional group.
 5. A lighting device as claimedin claim 3, wherein said controller means further comprises: means fordetecting whether any of said groups of light emitting diodes havebecome unable to pass between said energized light emitting state andsaid non-energized state, and transferring said groups to a thirdnon-functional group.
 6. A lighting arrangement comprising: two or morecircuit board means, each circuit board means having a projection axisand a plurality of light emitting diodes, such that any light emitted bythe light emitting diodes on each of said circuit board means isprojected substantially parallel to said projection axis; said circuitboard means being disposed such that each of said projection axes aredisposed at an angle to each other.
 7. A lighting arrangement as claimedin claim 6, wherein said angle is from 5 to 15 degrees.
 8. A networkcomprising: a host computer; and a plurality of light emitting diodelighting devices; said host computer comprising: means for transmittinga request for a status report from each of said light emitting diodelighting devices. and means for transmitting a signal to each of saidlight emitting diode lighting devices such that the host computer candirect how much light each of said lighting devices emits; and each ofsaid plurality of light emitting diode lighting devices comprising:means for receiving a request for a status report from said hostcomputer, creating said status report, and transmitting said statusreport to said host computer; and means for receiving a signal from saidhost computer and altering how much light said light emitting diodedevice emits in response to said signal.
 9. A network as claimed inclaim 8, wherein said status report comprises current luminositysetting, current actual luminosity output, current light emitting diodedegradation, current dirt accumulation, current number of light emittingdiode groups in use, current number of open-circuited light emittingdiode groups and current average usage time of light emitting diodegroups;
 10. A network comprising: a host computer; and a plurality oflight emitting diode lighting devices; said host computer comprising:means for transmitting a signal to each of said light emitting diodelighting devices such that the host computer can direct how much lighteach of said lighting devices emits; and each of said plurality of lightemitting diode lighting devices comprising: means for receiving a signalfrom said host computer and altering how much light said light emittingdiode device emits in response to said signal.
 11. A dirt detectionsystem for a transparent surface, comprising: an electromagneticradiation emitting means for emitting light; electromagnetic radiationmeasurement means for measuring light; said electromagnetic radiationemitting means and said electromagnetic radiation measurement meansbeing configured such that said electromagnetic radiation emitting meansemits a certain amount of electromagnetic radiation through saidtransparent surface, and said electromagnetic radiation measurementmeans measuring how much of said certain amount of electromagneticradiation is reflected by said transparent surface and comparing saidamount to a base measurement taken when said transparent surface is freeof dirt.
 12. A method for manipulating the light intensity in a tunnel,said tunnel comprising a lighting system comprising a plurality oflighting devices, said method comprising means for raising and lowering,in unison, the luminosity level of each of said devices